Electric welding is extensively used in the manufacture of a vast array of consumer and industrial metal products. When such products are made in a shop or plant an electrical power source to operate the welding equipment is always readily available. However, electric welding of field erected or constructed products is usually conducted at sites which lack a commercial source of electrical power so that it is necessary to resort to on-site generation of the required electric current by means of portable apparatus. Such apparatus will generally include a hydrocarbon fluid fueled engine to drive an electric generator, a fuel tank, ancillary transformers, controls and electric transmission lines to deliver the D.C. electric current at the proper voltage, amperage and hertz to the welding machines. Such equipment as presently used is both bulky and heavy and is expensive to transport, store and reposition at a construction site. It is also expensive so that if stolen or damaged the loss is substantial.
One substantial use of portable electric current generating apparatus is at construction sites where large vessels, tanks and similar metal shell structures are fabricated. When large cylindrical storage tanks are constructed they are generally made up of rings placed on edge one on top of the other. Each ring is usually made of a series of curved rectangular metal plates positioned end-to-end. When constructed as described, the vertical adjoining ends of the plates must be welded together. Additionally, the girth seams formed by the abutting horizontal edges of the rings must also be welded together. To make the described vertical and horizontal welds a suitable carriage is rollably supported on the top edge of the plates of each ring as it is installed. The carriage supports the required welding machine equipment and welding head. See U.S. Pat. Nos. 2,698,891; 2,742,554; 2,763,770; 2,794,901; and, 3,210,520.
The electric power needed to operate the carriage-supported welding machine equipment is produced on-site by a generator set mounted at ground level. An electric current transmission line extends from the generator set to the carriage. The transmission line must be long enough to accommodate movement of the carriage along the curved tank rings while the generator set is stationary so as to avoid moving the heavy generator set which, in use, weighs about ten tons. As a result, one or more expensive transmission lines, often two hundred and fifty feet long, must be used. The lines are heavy and constitute a serious burden and weight problem when the height of the tank increases as each ring is installed. Additionally, the transmission lines constitute a safety hazard and can be entangled with other construction equipment and be damaged or severed.
From the above it is believed clear that a need exists for an improved and lighter weight portable electric power source, and especially one which makes it unnecessary to use long transmission lines.